AP Chem Unit 0

Significant Figures & Dimensional Analysis

Placeholders (0s before the decimal place) & Magnitude

ARE NOT SIGNIFICANT (ex. 1570 has 3 sigfigs, not 4). The zeros are placeholders to report correct magnitude. Also, the same goes for zeros after a decimal place (0.00003 has 1 sigfig)

Which digits are significant?

• all nonzero digits are always significant

• zeroes between two nonzero digits are significant

• zeroes after the decimal point (or before the decimal point if there is a decimal point after)

  • 1240.0 has 5 sig figs, but 1240 has 3 sig figs

Scientific notation sig figs

• all digits except 10^n ARE SIGNIFICANT

  • ex. 1.406 × 10^6 has 4 sig figs

How many sig figs do exact numbers have?

INFINITE (ex. 5 test tubes = infinite sig figs)

Adding and subtracting with sig figs

• Answers are rounded to the least significant decimal place

ex. 11.67 cm + 5cm = 16.67

Multiplying or dividing with sig figs

• Answers are rounded to the number of digits that corresponds to the least number of sig figs in any of the numbers used in the calculation

Multistep calculations with Sig Figs

DO NOT ROUND INTERMEDIATES

• on each step, keep track of sig figs, and only round your final answer.

Density

• physical property of a substance

• units derived from the units of mass and volume

• density doesn’t depend on the AMOUNT of substance for pure liquids and solids

• its constant at a given temperature, so it can be used for identification of a substance

• higher density sinks; lower density rises

Metric System Prefixes

check your equation sheet - convert by multiplying by factors of 10 based on whats needed

“King Hector Does Usually Drink Chocolate Milk”